Hormone profiles of captive harp seals (Pagophilus groenlandicus) in relation to puberty, reproduction and senescence

Abstract

The main objectives of this study were to describe sex-steroid hormones in the harp seal (Pagophilus groenlandicus), in relation to seasonality in reproduction, puberty and senescence. Blood samples from 3 males and 2 females were collected at ~2 week intervals from 1999-2007. Plasma concentration of estradiol, progesterone and prolactin in females and testosterone in males were measured by radioimmunoassay. Estradiol in one mature female and testosterone in 3 males during their years of reproductive maturity increased across years roughly as would be expected from the breeding season of the wild Northwest Atlantic harp seal population. Estradiol and progesterone levels suggested that 1 young female did not reach maturity at 5 yr of age. Testosterone levels in 1 young male suggested that physiological maturity was reached at 4 yr of age. Estradiol levels in a mature female after she was ~22 yr of age declines substantially, suggesting senescence. This study extends our knowledge of reproductive physiology of phocid seals in general and the harp seal in particular, and shows that hormonal activities are not suppressed in the captive environment.